Abstract: A low-noise head amplifier has been developed for the extra low energy antiproton ring beam trajectory, orbit, and intensity measurement system at CERN. This system is based on 24 double-electrode electrostatic beam position monitors installed around the ring. A head amplifier is placed close to each beam position monitor to amplify the electrode signals and generate a difference and a sum signal. These signals are sent to the digital acquisition system, about 50 m away from the ring, where they are digitized and further processed. The beam position can be measured by dividing the difference signal by the sum signal while the sum signal gives information relative to the beam intensity. The head amplifier consists of two discrete charge preamplifiers with junction field effect transistor (JFET) inputs, a sum and a difference stage, and two cable drivers. Special attention has been paid to the amplifier printed circuit board design to minimize the parasitic capacitances and inductances at the charge amplifier stages to meet the gain and noise requirements. The measurements carried out on the head amplifier showed a gain of 40.5 and 46.5 dB for the sum and difference outputs with a bandwidth from 200 Hz to 75 MHz and an input voltage noise density lower than 400 pV/v Hz. Twenty head amplifiers have been already installed in the ring and they have been used to detect the first beam signals during the first commissioning stage in November 2016.

Abstract: A search for the doubly charmed baryon Omega(+)(cc) with the decay mode Omega(+)(cc) -> Xi K-+(c)-pi(+) is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb(-1). No significant signal is observed within the invariant mass range of 3.6 to 4.0GeV/c(2). Upper limits are set on the ratio R of the production cross-section times the total branching fraction of the Omega(+)(cc) -> Xi K-+(c)-pi(+) decay with respect to the Xi(++)(cc) -> Lambda K-+(c)-pi(+)pi(+) decay. Upper limits at 95% credibility level for R in the range 0.005 to 0.11 are obtained for different hypotheses on the Omega(+)(cc) mass and lifetime in the rapidity range from 2.0 to 4.5 and transverse momentum range from 4 to 15 GeV/c.

Abstract: Using proton-proton collision data at centre-of-mass energies of root s = 7, 8 and 13 TeV recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 9 fb(-1), the invariant mass spectrum of J/psi pairs is studied. A narrow structure around 6.9 GeV/c(2) matching the line-shape of a resonance and a broad structure just above twice the J/psi mass are observed. The deviation of the data from nonresonant J/psi-pair production is above five standard deviations in the mass region between 6.2 and 7.4 GeV/c(2), covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow X(6900) structure are measured assuming a Breit-Wigner lineshape.

Abstract: First evidence of a structure in the J/psi Lambda invariant mass distribution is obtained from an amplitude analysis of Xi(-)(b) -> J/psi Lambda K- decays. The observed structure is consistent with being due to a charmonium pentaquark with strangeness with a significance of 3.1r including systematic uncertainties and lookelsewhere effect. Its mass and width are determined to be 4458.8 +/- 2.9(-1.1)(+4.7) MeV and 17.3 +/- 6.5(-5.7)(+8.0) MeV, respectively, where the quoted uncertainties are statistical and systematic. The structure is also consistent with being due to two resonances. In addition, the narrow excited Xi(-) states, Xi(-)(1690) and Xi(-)(1820)(-), are seen for the first time in a Xi(-)(b) decay, and their masses and widths are measured with improved precision. The analysis is performed using pp collision data corresponding to a total integrated luminosity of 9 fb(-1), collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV.

Abstract: The main aim of this work is to present a simple method, based on analytical expressions, for obtaining the temperature increase due to the Joule effect inside the metallic walls of an RF accelerating component. This technique relies on solving the 1-D heat-transfer equation for a thick wall, considering that the heat sources inside the wall are the ohmic losses produced by the RF electromagnetic fields penetrating the metal with finite electrical conductivity. Furthermore, it is discussed how the theoretical expressions of this method can be applied to obtain an approximation to the temperature increase in realistic 3-D RF accelerating structures, taking as an example the cavity of an RF electron photoinjector and a traveling wave linac cavity. These theoretical results have been benchmarked with numerical simulations carried out with commercial finite-element method (FEM) software, finding good agreement among them. Besides, the advantage of the analytical method with respect to the numerical simulations is evidenced. In particular, the model could be very useful during the design and optimization phase of RF accelerating structures, where many different combinations of parameters must be analyzed in order to obtain the proper working point of the device, allowing to save time and speed up the process. However, it must be mentioned that the method described in this article is intended to provide a quick approximation to the temperature increase in the device, which of course is not as accurate as the proper 3-D numerical simulations of the component.